1. Field of the Invention
The present invention relates in general to automatic washing machines using low frequency vibration in clothes washing and, more particularly, to an improved structure in low frequency oscillating discs of such washing machines for both generation of strong circulation currents suitable for improvement of the washing effect and prevention of vibration energy loss of the water.
2. Description of the Prior Art
In order to wash clothes in a conventional automatic washing machine using low frequency vibration, a low frequency oscillating disc placed in a washing tub generates a specified low frequency vibration which causes resonance phenomena in a multi-phase washing medium in the washing tub. Here, the multi-phase washing medium consists of water, detergent and air. The level of low frequency is specified in accordance with shape the of the washing tub, the shape of the oscillating disc and the mixing ratio of the multi-phase washing medium.
In the above washing machine, the desired mechanical washing effect is achieved by the micro air bubbles generated by cavitation of the oscillating disc or nonlinear vibration. Both the cavitation and the nonlinear vibration are generated in the multi-phase medium at the same time of generation of the resonance phenomena. The mechanical washing effect caused by the cavitation or the nonlinear vibration cooperates with a chemical washing effect caused by the detergent in the washing medium, thus to achieve the desired washing effect.
With reference to FIG. 1, there is shown a typical automatic washing machine using the low frequency vibration. The washing machine generally comprises a washing tub 1, receiving a multi-phase washing medium therein, and a low frequency oscillating disc 4 causing the resonance phenomena in the washing medium. The oscillating disc 4 is placed in the washing tub 1 and coupled to an actuator 2 through a shaft 3. The shaft 3 transmits the drive force of the actuator 2 to the disc 4 so as to drive this disc 4. The actuator 2, which is mounted on the outer bottom of the washing tub 1, is applied with an amplitude signal and a frequency signal from a signal oscillator 7. A signal amplifier 8 is placed on a line between the actuator 2 and the signal oscillator 7 for amplifying and varying the signals generated by the signal oscillator 7.
There is provided a gap between the inner bottom of the washing tub 1 and the disc 4 for allowing the disc 4 to vertically vibrate. A lid 9 is provided in the opening of the washing tub 1 for hermetically covering the opening.
In operation of the above washing machine, the low frequency oscillating disc 4 is driven by the actuator 2 in response to signals applied from the signal oscillator 7 to the actuator 2 through the signal amplifier 8. This disc 4 thus oscillates in order to cause the resonance phenomena in the multi-phase washing medium in the washing tub 1. Here, the desired mechanical washing effect is achieved by the micro air bubbles generated by cavitation of the oscillating disc or nonlinear vibration, which cavitation and nonlinear vibration are generated in the multi-phase medium at the same time of generation of the resonance phenomena. The above mechanical washing effect cooperates with the chemical washing effect caused by the detergent in the washing medium, thus to achieve the desired washing effect.
In the above clothes washing using the low frequency vibration, the signal oscillator 7 makes the oscillating disc 4 oscillate in an oscillation frequency band of 20-250 Hz, an amplitude band of 2-25 mm and a rotational amplitude band of 2.degree.-10.degree.. Here, the signal amplifier 8 amplifies current signals or voltage signals which are to be applied from the signal oscillator to the actuator 2.
It has been noted that the above washing machine has the following problems.
Since the oscillating disc 4 simply vibrates at a predetermined frequency in the washing medium in the washing tub 1 so as to vibrate the washing medium and to cause a water current in the washing medium, this disc 4 only causes a weak water current. In this regard, large clothes may fall to be circulated in the washing medium but simply may lie in the bottom of the washing tub 1 due to their own weight. The clothes also may be jammed in the gap between the oscillating disc 4 and the inner bottom of the washing tub 1. When the clothes lie in the bottom of the washing tub 1 and are jammed in the gap as described above, the washing effect of the washing machine will be deteriorated.
The conventional disc 4 has a simple circular disc structure and this makes the circulation current mainly generated about the gap between the simple disc 4 and the inner bottom of the washing tub 1. Such a partial generation of the circulation current causes the disc 4 to be applied with strong water resistance. In addition, a large amount of power will be required for vibrating the disc 4 to a level achieving the desired washing effect. This directly runs counter to the recent trend of seeking energy savings.
In clothes-washing of the above washing machine, the washing medium, which was transmitted with the vibration energy from the oscillating disc 4, bumps against the disc 4 and loses its internal energy or the vibration energy. Hence, the washing medium should be provided with new direction and new velocity for its motion. In order to provide the new direction and new velocity of motion for the washing medium, the disc 4 will be attended with additional kinetic energy loss.